Telemetering system

ABSTRACT

A telemetering system for providing indications of various states of an object, such as its position, motion or rate of rotation. A core of soft magnetic material comprising the inductance of a high frequency tuned circuit is influenced by the magnetic field of a permanent magnet that is affixed to said object and that moves towards and away from the core, respectively, with the magnetic field generated by said permanent magnet premagnetizing said core so as to affect the attenuation of the tuned circuit, thereby influencing an output signal that comprises an indication of a measured value, i.e., indication of the state of said object.

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[4 1 Aug. 29, 1972 [54] TELEMETERING SYSTEM 2,918,666 12/1959 Brower..340/ 195 [72] Inventor: Palle-Finn Beer, Lidingo, Sweden PrimaryExaminer-Thomas B. Habecker [73] Assignee: AGA Aktlebolag, Lldingo,Sweden Att0mey Larson, Taylor & Hinds [22] Filed: March 19, 1971 57 ABSCT [21] Appl. No.2 126,060 1 A telemetering system for providingindications of various states of an object, such as its position, motion[30] Forelgn Apphcatmn Pnomy Dam or rate of rotation. A core of softmagnetic material March 24, 1970 Sweden .3980 comprising the inductanceof a high frequency tuned circuit is influenced by the magnetic field ofa per- [52] US. Cl. ..340/195, 324/179, 331/165 manem magnet h i affixedto id bj ct nd th t Clmoves towards and away from the core respectively[58] Field Of Search ..340/ 195, 192; 324/174, 179; with the magneticfield generated by Said permanent 331/165 magnet premagnetizing saidcore so as to affect the attenuation of the tuned circuit, therebyinfluencing an [56] References cued output signal that comprises anindication of a mea- UNITED STATES PATENTS sured value, i.e., indicationof the state of said object.

2,907,991 10/1959 Allen ..340/195 3 Claims, 1 Drawing figure SATURATIONCAUSES OSCILLATION BACKGROUND OF THE INVENTION.

1. Field Of The Invention.

This invention refers to a telemetering system for indicating variousstates of an object, such as its position, motion or rate of rotation.In this connection, it is assumed that the object is affixed to at leastone magnetic source that generates a magnetic field.

2. Description Of The Prior Art.

Previously known magnetic position-indicating transducers operate on oneof many physical principles, for example an attraction force on amovable contact, voltages from a Hall generator element, or resistancechanges in a so-called field plate. Unfortunately, applying theseprinciples entails definite disadvantages, such as contact wear, lowoutput power, and the requirement of high field intensity.

SUMMARY OF THE INVENTION.

In contrast to these previously known magnetic transducers, it is acharacteristic of the transducer in accordance with the instantinvention that it provides high output power as the result of moderatefield changes, concurrently with no wear occuring on the transducer.

The invention is characterized in that the magnetic field generated bythe magnetic source is adapted to actuate a soft magnetic core which issurrounded by a coil included in a high frequency tuned circuit, withthe attenuation of said circuit being an inverse function of the fieldintensity induced in the core by said transducer. The degree ofattenuation of the core is adapted to control the transmission of atelemetering signal.

The transducer in accordance with the invention utilizes the property ofa soft magnetic material, such as an alloy of nickel and iron (mumetal), that its high frequency magnetizing losses are influenced by thepremagnetization of the material. In accordance with the invention, themagnetizing losses may both be generated and indicated by the softmagnetic material being included as the core of a coil that comprisesthe inductance of a high frequency tuned circuit. When this core is notsubjected to a premagnetization, the circuit will have high attenuation,which corresponds to a very low Q factor in the tuned circuit. If on theother hand the core is subjected to a premagnetization, the attenuationis reduced, which corresponds to an increase of the Q factor of thecircuit. The attenuation will have its minimum value when the materialhas become magnetically saturated. When material of high permeability isused, the state of saturation is reached with moderate magnetic fieldintensities.

In accordance with the invention, the effect described above is utilizedfor making a tuned circuit self-oscillate, and cease self-oscillating,respectively, in response to the degree of saturation of the core causedby a permanent magnet being moved towards or away from the core,respectively.

BRIEF DESCRIPTION OF THE DRAWINGS.

The invention will be described more specifically below with referenceto the accompanying drawing, which illustrates the system of theinvention with amplifying means which may be made to oscillate and whichhave their oscillating state controlled by a magnetic source In thisparticular case, the source that generates the magnetic field consistsof a permanent magnet 10 which is secured to a shaft 13 that isrotatable in bearings 11, 12. The shaft with the permanent magnet may bemade to rotate in arbitrary manner, and as an example the drawingindicates that an impeller 14 is fastened to the shaft and may berotated by a flow of fluid which is illustrated by means of arrows 15,for example water. The permanent magnet 10 is bipolarly magnetized withthe poles N and S as shown in the drawing. The field generated by magnet10 influences a magnetic core 16 which is surrounded by a coil 17. Thecoil is connected in parallel with a capacitor 19 over a line 18 whichmay consist of a coaxial line and forms a high frequency tuned circuitwith said capacitor, with said circuit being connected to the inputelectrodes, i.e., the base and emitter, of a transistor 21 over acapacitor 20. A second high frequency tuned circuit, which consists of acoil 22 and a capacitor 23, is connected to the output of saidtransistor and may be tuned to approximately the same resonancefrequency as the circuit 17, 19. Operating voltage is supplied to thetransistor from a terminal 24 over a resistor 25 to the collector viathe tuned circuit 22, 23 as well as over a resistor 26 to the base, sothat the latter will be provided with an appropriate bias. Finally theoutput circuit of the transistor 21 with respect to the high frequencygenerated in the self-oscillation is closed through a capacitor 27, withthe junction between this capacitor and resistor 25 being connected to aterminal 28.

The pertinent system operates as follows: When the magnetic fieldgenerated by the source magnet 10 premagnetizes the core 16 so as tosaturate or nearly saturate said core, the core will have practically noattenuating effect on the tuned circuit circuit 17, 19. Hence the latterwill have a very high Q factor. A capacitive coupling occuring intransistor 21 between the collector and the input circuit of saidtransistor can then cause the transistor to begin to self-oscillate,which-is facilitated by the two tuned circuits 17, 19 and 22, 23,respectively, being tuned to the same frequency. Self-oscillation isachieved when one pole, N or S, respectively, of the transducer magnetis directed towards core 16. In the intermediate position the magneticfield of the transducer magnet 10 will not affect the core 16, and asthe result of this the premagnetization of the core 16 will be reducedso that it will have a strong attenuating effect on the circuit 17, 19.This will cause the self-oscillation to cease immediately.

This system is highly insensitive to external electromagnetic andmechanical disturbances. Also, it is characterized by the reaction ofcore 16 on the source magnet 10 being extremely small, with the resultthat no apparent braking thereof occurs. This is the result of anextremely small change of field being necessary for providing a changein the oscillating state. Furthermore, the system rapidly follows thefield changes to which core 16 is subjected, and therefore it is capableof indicating high rotative rates of the source magnet. It may bepointed out simultaneously that the oscillating state of the transistoris responsive to the magnitude of the magnetic field that influencescore 16 and not to its rate of change. The system may therefore beutilized for indicating very low rates of rotation and it may also beutilized for providing indications of changes in position. it may bementioned that this result cannot be achieved by systems having theirfunctions responsive to the voltage induced in a coil.

In the system described above it has been assumed that the transistor ismade to begin to self-oscillate and to cease oscillating, respectively,twice per revolution of the transducer magnet 10. However, it ispossible to achieve one single change to self-oscillation and out ofself-oscillation, respectively, per revolution, for example if core 16is subjected to an appropriately selected fixed premagnetization. Suchpremagnetization may be provided by means of a magnet 29 which isindicated by broken lines in the drawing and which may be adjusted such,with respect to core 16, that its effect on the premagnetization of thecore may be controlled.

The high frequency generated in the self-oscillation may be utilizeddirectly for providing an indication of the position and rate ofrotation, respectively, of the source magnet ll). For doing so, the highfrequency oscillating energy may be extracted at the collector of thetransistor and may be fed directly or over a high frequency amplifier toan antenna or, if desired, to a high frequency transmission line. Also,the system is capable of transmitting two different voltage levels as anoutput signal in response to the instantaneous saturation state of core16. This is based on the following function.

When transistor 21 is not self-oscillating its base will have a positivevoltage with respect to the emitter as the result of resistor 26 beingconnected between terminal 24 and the base. Hence, the transistor willbe conductive, and a comparatively heavy current will pass resistor 25so that a predetermined lower voltage level will be maintained overcapacitor 27 and therefore between terminals 23 and 30. Whenself-oscillation has commenced, the current through transistor 21 andthus also through resistor 25 decreases, and as the result thereof thevoltage between terminals 28 and 30 will be set to a higher lever. Thedifference that thus is created between the voltage levels at terminal28 will be of such magnitude that it immediately can be utilizeddirectly for providing an indication or for remote transmission of thecorresponding measurement value.

The description above has disclosed an embodiment of the invention inwhich core 16 is influenced by the variable magnetic field of a rotatingpermanent magnet. However, it may be taken from the above that theinvention is not bonded to this specific embodiment and that the systemalso may be utilized for providing an indication of the position of amagnetic source with respect to core l6. If furthermore a moving object,for example a conveyor line, is provided with a great number of magnets,its motion may be indicated by these magnets passing the core of thetuned circuit one after another and successively making the tunedcircuit self-oscillate and cease self-oscillating, respectively.

It is also possible to place core 16 in coil 22, which is included inthe output circuit of the amplifier, so as to attenuate said tunedcircuit whereby the oscillating conditions of the amplifier will becontrolled in response to the magnetic field generated by source 10.

l. X telemetering system for indicating various states of an object,such as its location, motion or rate of rotation, comprising a. magneticsource means for generating a magnetic field affixed to said object,

b. soft magnetic core means,

c. first tuned circuit means including a first coil that surrounds saidcore means,

d. amplifier means having an input and an output,

respectively, and

e. second tuned circuit means including a second coil,

said first tuned circuit means being connected to the input of saidamplifier means for making said am plifier means self-oscillate inresponse to the state of magnetization of said core means caused by saidmagnetic field and said second tuned circuit means being connected tothe output of said amplifier means, with the attenuation of said firsttuned circuit means being an inverse function of the field intensityinduced in the core means by said source means and with the signaltransmitted from the telemetering system being responsive to the degreeof attenuation of said core means.

2. A system in accordance with claim 1, wherein said source comprises apermanent magnet which is affixed to a rotatable member and whichprovides an angularly responsive premagnetization of the core means soas to cause the amplifier means to self-oscillate and to ceaseself-oscillating, respectively, one or more times per revolution of saidrotatable member.

3. A system in accordance with claim 1, wherein a direct currentsupplied to the amplifier means generates a voltage drop over a resistorwhich at a ter minal to which the resistor is connected provides avoltage with a level responsive to the oscillating state of theamplifier.

1. A telemetering system for indicating various states of an object,such as its location, motion or rate of rotation, comprising a. magneticsource means for generating a magnetic field affixed to said object, b.soft magnetic core means, c. first tuned circuit means including a firstcoil that surrounds said core means, d. amplifier means having an inputand an output, respectively, and e. second tuned circuit means includinga second coil, said first tuned circuit means being connected to theinput of said amplifier means for making said amplifier meansselfoscillate in response to the state of magnetization of said coremeans caused by said magnetic field and said second tuned circuit meansbeing connected to the output of said amplifier means, with theattenuation of said first tuned circuit means being an inverse functionof the field intensity induced in the core means by said source meansAnd with the signal transmitted from the telemetering system beingresponsive to the degree of attenuation of said core means.
 2. A systemin accordance with claim 1, wherein said source comprises a permanentmagnet which is affixed to a rotatable member and which provides anangularly responsive premagnetization of the core means so as to causethe amplifier means to self-oscillate and to cease self-oscillating,respectively, one or more times per revolution of said rotatable member.3. A system in accordance with claim 1, wherein a direct currentsupplied to the amplifier means generates a voltage drop over a resistorwhich at a terminal to which the resistor is connected provides avoltage with a level responsive to the oscillating state of theamplifier.